Fluid Dynamics in Microgravity
Nick YoungNaomi Todd
Kevin Shump
Joe Intile
Tualatin High School / Chris Murray (Instructor)
Nancy Rabel Hall (Advisor)
Introduction
A common area of study in microgravity deals with unhindered capillarity. In the presence of gravity, fluid in a tube will rise to a specific height based on the contact angle, surface tension, and diameter of apparatus (Giancoli 1998, p. 296.). In microgravity, capillary tubes can be used to pump liquids the entire length of the tube (Stange, et al. 2003, Siegel 1961, NASA CAPL-2, 2004, ZARM 2004). In April of 2005 (Tualatin High School Physics, 2005), a group of students used capillarity with water to eject droplets into the air with limited results due to the wetting characteristics of water and glass. Therefore, we intend to use silicone fluids and small geometries to obtain more consistent results. We propose to use this capillarity to investigate three different fluid experiments dealing with liquid dynamics in microgravity, related to creating droplets in microgravity. The two experiments will deal with tubes that are tapered to varying degrees, and capillary flow through an hourglass shaped tube and through tubes of differing diameters.
With the tubes with different diameter exit openings, we hypothesize that only the smaller openings will actually eject the droplets, and the larger openings will not have sufficient momentum to overcome the surface tension and adhesion with the tube.
Regarding a restricted tube, like the hourglass shape, we are expecting the velocity of the liquid to increase as it approaches the point of restriction. At the point of greatest restriction, we hypothesize that the velocity will be great enough to propel a droplet into the air within the tube above the constriction.
Method
Our apparatus consisted of three 1/8 inch thick acrylic tubes 8 inches tall with an inner diameter of 2 inches solvent welded to a 3/8 - inch base. At the base of the tubes, the inner diameter was reduced to 1 ¾ inches by a 1. 3/8 inch tall piece of 1/8 wall tubing to provide a pinning edge around a reservoir with a capacity of approximately 50 ml.
Picture of the three cells holding three experiments.
Inside each cell, suspended by the lid of the cell on a holding bar, are the capillary tube experiments themselves, and the whole thing was protected by an outer box with a lid that screwed shut.
The whole thing /
One of the holders with a tube
The cells were filled with 50 ml of DOW 200 .65 cSt fluid with a blue dye added and filmed with a 640x480 30 frames per second video camera against a backlight. The whole apparatus was dropped in the NASA Glenn Research Center 2.2 drop tower. We then analyzed the height of the fluid frame by frame from the video.
The cells backlit /
A Frame of video showing the liquid